Vinyl polymers, in particular (meth)acrylic polymers, having a crosslinking silyl group(s) within the molecule are used in highly weathering-resistant coatings utilizing the high weathering resistance owing to the main chain and crosslinking point(s) thereof. These (meth)acrylic polymers are generally produced by copolymerizing a (meth)acrylic monomer having a crosslinking silyl group(s) with another monomer or other monomers and, therefore, crosslinking silyl groups occur randomly in the molecular chain. It is thus difficult to use them in lieu of rubbers. On the other hands, attempts have been made to produce crosslinking silyl-terminated (meth)acrylic polymers and use them in sealing or adhesive compositions. As for the production of crosslinking silyl-terminated (meth)acrylic polymers, Japanese Kokoku Publication Hei-03-14068, for instance, discloses a method which comprises polymerizing a (meth)acrylic monomer(s) in the presence of a crosslinking silyl-containing mercaptan, a crosslinking silyl-containing disulfide and a crosslinking silyl-containing radical polymerization initiator, and Japanese Kokoku Publication Hei-04-55444 discloses a method which comprises polymerizing an acrylic monomer(s) in the presence of a crosslinking silyl-containing hydrosilane compound or a tetrahalosilane. Further, Japanese Kokai Publication Hei-06-211922 describes a method of producing crosslinking silyl-terminated (meth)acrylic polymers which comprises synthesizing a hydroxyl-terminated acrylic polymer using a hydroxyl-containing polysulfide in excess of an initiator and further converting the hydroxy group(s).
As a general method of introducing a crosslinking silyl group into a polymer terminus or termini, there may be mentioned the use of the hydrosilylation reaction involving a polymer terminus alkenyl group(s). However, compounds having both a silanol group and a hydrosilyl group are unstable and difficult to obtain and, therefore, it is difficult to introduce a silanol group(s) into a polymer terminus or termini by this method.
On the other hand, among crosslinking silyl groups, the silanol group is highly reactive and frequently used in the field of silicones, in particular, utilizing its high reactivity. However, almost no silanol-terminated polymers other than silicones are known since the production thereof is difficult as discussed above.
Further, among crosslinking silyl groups, ketoximo groups, acyloxy and like groups are highly reactive and are frequently used in the field of silicones, in particular, utilizing their high reactivity. However, almost no ketoximo- or acyloxy-terminated polymers other than silicones are known since the production thereof is difficult as discussed above.
Meanwhile, it is known that alkenyl-terminated polymers can crosslink by themselves or be crosslinked by using a curing agent such as a hydrosilyl-containing compound to give curing products excellent in heat resistance and durability. As the main chain skeletons of such polymers, there may be mentioned polyether polymers such as polyethylene oxide, polypropylene oxide and polytetramethylene oxide; hydrocarbon polymers such as polybutadiene, polyisoprene, polychloroprene, polyisobutylene, and hydrogenation products derived therefrom; polyester polymers such as polyethylene terephthalate, polybutylene terephthalate and polycaprolactone; and polysiloxane polymers such as polydimethylsiloxane, among others, and these are used in various fields according to the characteristics of the respective main chain skeletons.
(Meth)acrylic polymers have those characteristics which other polymers such as mentioned above cannot have, for example high weathering resistance and heat resistance, oil resistance and transparency, and the use of some having an alkenyl group(s) on a side chain(s) in highly weathering resistant coatings has been proposed (e.g. Japanese Kokai Publication Hei-03-277645, Japanese Kokai Publication Hei-07-70399). However, alkenyl-terminated (meth)acrylic polymers are difficult to produce, hence have hardly been put into practical use.
Japanese. Kokai Publication Hei-01-247403 discloses a method of producing acrylic polymers having an alkenyl group at both termini which uses an alkenyl-containing dithiocarbamate or diallyl disulfide as a chain transfer agent.
Further, Japanese Kokai Publication Hei-06-211922 discloses a method of producing alkenyl-terminated acrylic polymers which comprises producing a hydroxyl-terminated acrylic polymer using a hydroxyl-containing polysulfide or an alcohol compound as a chain transfer agent and further utilizing the reactivity of the hydroxyl group.
On the other hand, curable rubber-like elastomer compositions are widely used as adhesives, sealants and shock absorbers. According to the curing means, these are roughly classifiable into the so-called moisture-curable compositions which are stable under tightly closed conditions but cured by the action of moisture at room temperature to give rubber-like elastomers and compositions undergoing the crosslinking reaction upon heating, for example through the hydrosililation reaction.
However, it is difficult by the methods mentioned above to introduce an alkenyl group terminally into a polymer with certainty. Further, these methods generally use radical polymerization and, therefore, the polymers obtained have a broad molecular weight distribution (ratio of weight average molecular weight to number average molecular weight), which is generally not less than 2, and, accordingly, show a high viscosity, which is a problem. When the viscosity is high, problems arise, for example handling in application as a sealing agent or adhesive, for instance, becomes difficult or it is impossible to incorporate a large amount of a reinforcing filler.
Furthermore, it is not easy to introduce a radical-polymerizable acrylic functional group into (meth)acrylic polymers polymerized by radical polymerization. In particular, almost no oligomer compounds with an acrylic functional group introduced terminally thereinto have been synthesized.
On the other hand, in photocurable compositions, low-molecular compounds having an acrylic functional group(s) are used in many instances. In this case, the odor resulting from evaporation of low-boiling unreacted compounds during and after curing is a great problem. For avoiding this problem, oligomers having an acrylic functional group(s) are used. However, mainly from the synthesis viewpoint, such oligomers are restricted to the epoxy-acrylate, urethane-acrylate, polyester-acrylate and like types, and few oligomers having a high molecular weight are available. As a result, the curing products derived from them tend to become relatively hard ones. Any products having good rubber elasticity cannot be obtained.